Autopilot force link



May 8, 1962 s. J. slKoRA AuToPILoT FORCE LINK 2 Sheets-Sheet l Filed April 25, 1960 N .mi

INVENTOR` STEPHEN J. SlKORA AGENT May 8, 1962 s. J. SIKORA 3,033,495

AUTOPTLDT FORCE LINK Filed April 25, 1960 2 Sheets-Sheet 2 7o es s? AERoDYNAMIc j SwASH 1'" RESPONSE PLATE I l I I e1 i s3 gf l 1 75 sa I 71 I 12 y FITCH HYDRAuLIc R I DoDSTER GYRO AMPLIFIE l l I e? l 100 54 rf FFEDBACK MECHANICAL DIFFERENTIAL 10i-1,

FoLLow-UP f4 1o FoLLowER I 94 so`l lg. 2

e1l INTEGRATDR 701 122\ 126? AERoDYNAMIc TAIL RoToR L HYDRAULIC f' RESPONSE PITcH aoosTER 1302 i :,125 HEADING 124 l REFERENCE 7 l -GYRD 135 v 121 MECHANICAL 134 137 38 mf 132 133 13s DIFFERENTIAL 55 154 AMPLIFIER I 159 159 152 I e 156 I Y i i /143 M2 14o, "T I-123 1 53 151 I-1so 15o- FEEDBACK JI DYNAMIC 14ML vERTIcAL GYRo FoLLow-UP ,4 ,0

FoLLowER F/g 4 153 ISI l 162-1 INTEGRATDR INVENTOR.

STEPHEN J. SIKORA AGENT United States Patent O.

AUTOPILQT FORCE LINK Stephen J. Sikora, Warminster, Pa., assignor to the United States of America as represented by the Secretary of the Navy Filed Apr. 25, 1960, Ser. No. 24,633 11V Claims. (Cl. 244-76) (Granted under Title 35, U.S. `Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to aircraft control systems, and more particularly the invention relates to an automatically and manually operated aircraft control system.

An object of this invention is the provision of novel Vmeans for establishing a new attitude reference for an aircraft in the pitch, roll and yaw axes Without switching the automatic pilot off but Iby merely manipulating the manual controls.

Another object of the invention is the provision of a novel force link for use in an aircraft adapted to be manually and automatically controlled, the force link permitting the attitude of the aircraft to be changed by the mere `manipulation of the manual controls and for establish` ing new attitude references in the pitch, roll and/ or yaw axes Without switching olf the automatic pilot.

Yet another object of the invention is the provision of i a novel force link for use in the control linkages of an aircraft and more particularly in a rotary wing aircraft, wherein the automatic pilot need not bel switched off in order for a new aircraft attitude to bevestablished in the pitch, roll and yaw axes, the autopilot continuing to maintain the aircraft at the newly' established attitude after the manual controls have been released.

Another object of the invention is the provision of a novel compact and simple electromechanical force link suitable for use in the pitch, roll and yaw channels of an autopilot. l

of whether the force link has been contracted or elongated. Y

A still further object of the invention is the provision of a means for feeding a signal back to the input of an autopilot servomeehanism which is proportional to the length of time that the force link is elongated or con-l tracted, as set forth in the preceding object, algebraically -multiplied by the magnitude of the elongation or contraction of the force link, the algebraic product of the time and displacement magnitudes being integrated and 3,033,495 Patented May 8., 19672 ice represent corresponding parts throughout the several views, and in which:

FIG. 1 is a longitudinal sectional view of a force link device; 5'

FIG. 2 is a schematic electromechanical diagram of an automatic pilot and manual aircraft control system embodying the invention for controlling an aircraft about either the pitch or roll axis of the aircraft;

FIG. 3 is a schematic electromechanical diagram'of the preferred form of'an integrator shown in FIG. 2; and

FIG. 4 is a schematic electromechanical diagram of an automatic pilot and manual aircraft control system embodying the invention for the yaw aXis of an aircraft.

t is to be lunderstood that the invention is notlimited to the details of construction and arrangement of parts shown in the drawings Yand hereinafter described in detail, but is capableof being otherwise embodied and of being practiced and carried out in various-ways. It is to be further understood that the phras'eology or terminology employed herein is for the purposeof description and there is no intention to herein limit the invention beyond the requirements for the prior art` Referring to FIG. l, a device embodying invention and hereinafter referred to` as a force link is indicated generally by the reference numeral 10. The force link 10 comprises a housing 11 having an eye 12 threaded into and fixed with a lock nut 13 to a closed end 11a Qthereof, and a plunger assembly, indicated generally by fed at a predetermined rate to the input of the servo- I mechanism of the autopilot.

The invention further resides in certain novel features i of construction, combinations and arrangements ofgparts,

and further objects and advantages of the invention will be apparent to those skilled in the art to which it per- -tains from the following description of the preferred embodiment thereof, described with reference to theY accoml panying drawings inwhich similar reference characters the reference numeral 14. The plunger assembly 14 comprises a rod endniember 15 having an eye 16 at oneend thereof and an internally threaded nut portion 17 threaded onto the outer end of a cylindrical actuating .shaft 18.

The actuating -shaft 18 is threaded 'throughout approximately half of its length and extends a substantialrdistance inside of the housing 11 so that a flanged end portion 1,9 thereof is normally substantially coplanar with an internal' annular shoulder portion 20 located substantially two-thirds from the outer open end 21 'of the housing 11. The housing 11 is formed with a rectangularopening 22 in the bottom or closed end 11a and with a cylindrical bore or Wall 23 forming the balance of the in- 'ternal wall of the cup-shapedhousing 11. The outer end of the wall 2-3`is internally threaded so as to receive an externally threaded adjustable preloading screw 25 which vhas a hexagonally-shaped radial flange 26 at the outer end thereof. The preloading screw 25 has al central cylindrical opening 27 and a counterbore portion 28 so as to reduce the sliding friction between the preloading screw 25 and a hollow shaft sleeve 30.

The actuating shaft 18 has a central cylindrical passage 31 for receiving an armature positioning rod 32 which on the extreme inner end thereof carries a variable impedance transformer core 33 movable with respect to the fixed windings of a variable impedance transformer 34 fixed in the bottom of the housing 11 and conforming to the shape `of the Wall 22 of the housing 11. The outer end of the armature positioning rod 32 is slotted for a screwdriver and is provided with a lock nut, 35

threaded thereon lso as to permit the armature 33 to be adjusted to` a zero output or central position within the jtransformer 34 an-d then locked in position.

spring retaining washer 43. t The backside of the-Washer 43.is.sl10.wn engaging the terminal. inner ends of thepreloading screw 25 and the sleeve 36, FIG. l.

The spring 4Z is preloaded by adjusting the preloading screw so that aA load of preferably 50 pounds per inch of displacement is required to elongate or contract the force. link 10, It isV tobe. understood, however, that the preload of the spring 42 can be set at any force so that when a predetermined force is exerted against the force link 10, the-force link is contractedl or extended by compressing. the spring 42.. Therefore, the forceV link 10 will transfer forces upto 50 pounds, and any load thereover will cause relative axial displacement of the core'within the transformer 34.

A lock nut Si? is providedA on the preloading screw 25 sothat the preload adjustment canibe maintained. Also, a selected preload adjustment of theY sleevetl is attained by. means. of an adjustable Prelcading. nut 5.1- The nur 5 1 isthreaded. ontoztheouter endA of. the actuating shaft 1- 8 s o as to adjust vthe relative position ofthe sleeve 30 on the actuating shafblS. Arlock nut` 52is provided -for looking: the adjusting nut. Si in'place on the actuating shaft 1,8. Thescrews 2S' and 5.1, respectively, limit the totalamoun't which thelforce link ltlcan be extended and retracted. i i V "Referring to FIGS 2 and 4, the force link 10 can be connected. inr any push-pull, linkage in an aircraft control system. Although, the invention will be described in connection with an helicopter control system, it is understood'th'atithe force link can be 'used' in any aircraft controll system, wherein an autopilot and/or a stability. augnientatio'nsystem Iis being utilized. Theactual location ofthe 'force' links, iny an helicopter rotor pitch control system as lWelll "as ina cyclicpitch or Vroll control systenif'for. `controlling a swash plate, can be in any of a nun'i'be'r` -ofplaces where there isa push pull relationship. For'exa'mple, one end of the force Ilink may be ixed to a crankv arm. of .an autopilot. servomotor and the other end lxcdf'to'a'fbell crankin. a manual controlsystem where the `control.motion of the'co'ntrol stickfor pedal is trans- ;-b'y'means ofsomefform of shaft rotation. Alv ely, if there is,l push-pull linkage.` in the Vaircraft l``syS'.ttSri1,`thel force flink canV be.. directly incoru orcelink 19, by meansgof the eyes 12 and 16.

In the' eyclicpitch sw'ash plate contro-lI 'system` of, a helicopter, FIG. 2; the force link lo" has one end xed toay rank arm/6110i a servomotor 61 with the other eid;y Yx'ecl toa bellcrank 62.0perated by a pilots cyclic pitclhcolitrol stick 63. -Motion`of the bellcrank 62 is tiarisrnitte'dl tor a mechanical differential via a push-pull rodfffor'ch'alnging'the pitch of a swash plate 616,. vMotri from the diiferentialV 6,4 'is preferably transmitted through a push-pull linkage I67, which has a 'conventionalhydraulic boostenunitf therein. Movement of. the silvash plate oo causes aerodynamic response in the helicopierP fuselage 70, which is yschematically illustrated.

' The autopilot4 inFIG. 2 isprovided with a vertical disp/lac'ement"V gyro 71 which reacts in responsevto any*` helle ter fuselage deviation vertically fromfa reference plane. ""Accordin'gly, any. deviation ofthe helicopter fuselage, 70, from thel reference planercauses .the gyro 71 to generate an electrical output signal ofy aphase depending uponwhether fuselage displacementis taking place in a.

vertically upwardly, or a vertically downwardly direction.

The magnitude. ofv the. signalis, representative of the 5 amount of fuselage pitch and is fed yfrom' the vertical ted b'y merelybr'eam'ng'the linkage 'andinsertin to the mixing point '72 in series with the `amplifier 75 71 to aimixing pointiTZl byv means of. anelectn'cal connection 73. Fromthe mixing point 72, therdisplacement rsignal-from the gylQ '71 feeds intoan amplifier 75 -by :means *of anfelectrical conduitA 74." "The output of the'k amplifier 75 isgfed via an electrical conduit. 76A to energize and excitethe ysynchronous,servornotor 6 1.

Mixing pointV 72l is a,cmiventional electrical juncture where the variousvvoltages maycombine. In ,itsV simplest form'it is a point Wherethe output conductors from elements 71, 100, 101, and Si) form. a. common juncture. In its most complicated -form mixing point 72 would be composed of resistors and capacitors `arranged to insure proper phase and gradient relationships of the outputs from elements 71, lill?, 1,01,Y and 80. For purposes of thisinvention,howevenritvinay be' assumed that the outputs from'thevelementsvare ofl proper phase and gradient relationships.

Should the helicoptery beon a normal horizontal course and the pilot decide. to nose-up the helicopter fuselage 70. by Operating th. Qylritchlstk @3., itis necessary for the pilot to overcome the resistive force of the spring A42d so as to cause, for example, theretraction of the force -linkv 1t). lflccordingly, the core 33- moves to the left,

'184 ofthe samev voltage but ofr'opposite electrical phase.

The output ofthe integrator `Sois a function of the algebraic'product of the totalY time the force link 10g-is retracted multiplied by the magnitude of they total distance by which the armature has been` moved from its centralt null position relative toA the primary transformer windings 83- and 84. The .Output of the integrator Sois fed at alpredeterminedV rate tothe mixing. point 72.

Referring toiFlG. 3,the integrator 80 is comprised of an amplier 86having its inputs connected to the transformer pick-utf coil 824 and its output electrically connected' to a synchronous motor 87, which` ismechanically connected'tovdrive a generator unity 88. A pickoifl coil 89 ofa generator 8S feeds a nulling signal back into and in series with the input to the amplier 86l so that-the feedback is proportionalto servoshaft displacement and speedofj the synchronous Imotor 87. The' signal picked otbby, the` generator` coil v-89-is opposite in phase to that oftheseeondarywinding 82 of the transformerv 34, A drive shaft 91B of the Synchronous motor 87` positionsa rotor clarryingan input coilz91-Vv of a, synchro transmitter 92 and.;-tfaasrr1ts a Sisnalbya. Sewadary winding 9.3. which is Preferably. Yrshaped- The transmitter-Winding 93 feeds a signal, proportionalto the product oftime and, magnitude of relative Vdisplacement of-the core 33,

via leads 94, 74.. The output of the synchromotor 8,7 isnulled because the signalpickedotf from the winding 8.9 is in opposition to the signal -picked olf by the Winding 82 andaeeordingly, when the sum of the two signals is Zero, the output of the amplifier 836 isnulled.

VInoljder; that the output of the servomotor 61 be nulled fora given input fromthe cyclic pitch stick, a feedback unitli) is v provided for nulling the output of the amplifier 75.k Furthermore, in order to prevent overrun and hunting oftl 1 e.servon 1otor 6i a followup follower unit 101 is provided in parallel with the feedback unit 169. The feedback-unit 10]) langl-tigre followup. follower unit 1011 are similar to those found in the U.S.' Patent No. 2,919,384

issued December 29, 19.59, to Louis'S. Guarino and Wil-V liam M. Ogdenr for a Helicopter lAutomatic Engine Speed Selector and-Control. Alternatively, the feedback and followupfollower unit y10i), 101 may 'be similar to that disclosed in copending patent application entitled Stability Augmentation Systern by Stephen T.` Sikoraand Louis S. Guarino, application Serial No.y 862,7 30, tiled December 29, 1959.

Referring to IFIG. 2, shouldl a gust ofWind Cause the helicopter. 701S11dde111y Pitch up, @proportionate displacement signal isfedy to the amplifier 75via the leads 73, Mofronl the displacementgyro71. Should the pilot simultaneously desire. to Apitch upthehelicopter 70 vby a. slightly greater degree, the cyclic .pitch stick 63'is pulled backjand th. `'force link 10 iscontracted.v As. a,resu1t,f a signal is fed from the transformer 34 via theintegrator 80 to the mixing point 72. lNow since the aircraftfis al` ready inadvertently nosed-up by the gust of wind, the signal from the integrator S0, which has been picked olf from the Iforce link 10, will be in oppositionto the signal from the vertical displacement gyro 71 and the difference of vthat signal will be transmitted to the amplifier 75. Since it is desired to nose the aircraft up slightly more than that which has been inadvertently caused, only the difference between the signals from the vertical gyro 71 and the integrator 8i? will` be fed to the yservo motor 61 for causing a signal to be transmitted via force link mechanism 10land the link 65 to the mechanical diierential 464 and accordingly toslightly pitch up'the swash plate 66. Conversely, if the helicopter hadhaccidentally or inadvertently pitched down dueto ambient atmospheric conditions, the signals from the Yvertical gyro 71 and the integrator 80 would be additive and accordingly the sum of the signals would be fed tothe amplifier 75.

Referring to FIG. 4, an automatic and manual control system for the yaw axes of the helicopter is schematically illustrated. The system is comprised of a force link 10 adapted to transmit control motion from a crankV arm 121i of a synchro motor -121 to a tail rotor pitch control mechanism '122 via a push-pull linkage `123, a mechanical differential 124, and a shaft linkage 125, which preferably has van hydraulic booster unit 126 therein. Change of the pitch setting of the tail rotor causes aerodynamic response vof the helicopter fuselage 70. The synchro motor 121is'energized by an error signal generated by a heading reference gyro' unit 130 and transmitted via electrical conduitsf131, l132, a switch 133 normally closed with acontact 134, a mixing point 135, an4 electrical conduit 13'6, an amplifier 137, and an amplifier output conduit' 138. The output of the amplifier 137 'is nulled by means o f'a feedback mechanism 140. Overrun and hunting of the servo motor 121 is eliminated by means of a followup `follower mechanism 141 connected in parallel with the feedback mechanism 14%. Signals are picked o from the' servo motor 121 and vfed to the mechanisms 140, 141

via aline 142. rlhe outputs of the mechanisms 140, 141

ably, whenever .a roll of greater than four degrees in either direction is .experienced by the helicopter and when the airspeed preferably exceeds thirtyv knots. More particularly, a roll synchronizing servo mechanism 151 is adapted to move switch 13-3 to contact 152 when the helicopter fuselage roll exceeds four degrees in eitherV direction. An airspeed servo mechanism 153 moves a switch 154 from contact i155 to Contact 156 when the airspeed exceeds thirty knots. the tail rotor is controlled by the dynamic vertical gyro Operation of rudder pedals `159 schematically shown in FIG. 4, causes the extension or contraction of the force link 1t) via a crank arm 160. The signal picked olf at the'force link 10' is fed to an integrator 161 via line 162. The output of the integrator 161 feeds to the mixing point 135 via a line 163. The integrator 161, the feedback mechanism 140 and the followup follower mechanism 414-'1 of FIG. 4 are respectively similar to the integrator p80, thefeedback mechanism 100 and the followuplfollower mechanism 101 of FIG. 2. Aglimift'switch 17d is located Within the housing `11,

"'FlGffLand adapted to :be actuated by axial movement Accordingly, the pitch of While several specific embodiments in accordance with the invention have been shown and described, it is understood that the invention issusceptible of many changes andinodications, as known to persons skilled in the art, and is intended to cover all such changes and modifications coming within the scope of the appended claims.

What is claimed is:

l. In an aircraft having a control surface, the' combination comprising manual control means including pushpull means for operating and controlling said control surface, automatic pilot meansincluding displacement gyro means adapted -to generate an electrical error signal proportional to the displacement of the aircraft from an established reference attitude, amplifier means, circuit means electrically connectingsaid amplifier means to saidv gyro means, synchro motor means electrically connected to the output of said amplifier means and having a crank arm operating said push-pull means, force link means connected in said push-pull means for transmitting mespring loaded plunger therein for permitting said force link means to be contracted and elongatedby override command movement of said manual control means, variable impedance transformer meansin said housing having a core adapted to be axially displaced whenthe length of said force llink means is. changed for picking olf an electrical command signal representative of change of force linklength and the duration the length of said force link means 4is changed, integrator means connected to integrate said command signal, said integrator mea-ns having lan output electrically connected to said mixing junction in opposition .to saidelectrical error signal ofsaid gyro means, 4said f integrator means supplying said electrical command signal to said junction at a predetermined rate, an electrical-command signal of one phase being picked off from said transformer means and fed -to said integrator' when said force link means is contracted and an electrical command signal of an opposite phase :being picked off Whensaid force link means is extended upon the manipulationof said manual control means for "overriding said automatic pilot means.v

f 2. In an aircraft having a control surface, the combination comprising'm-anual control means including pushpull means for operating and controlling said control surface, gyro means adapted to generate an electrinal error signal that is a function `of the displacement of the aircraft from an established reference condition, ampli-l fier mean-s, circuit means electrically connecting said ampliiier'means to said gyro means," synchro motor means driven by the output of said amplierjmean-s and having a crank arm operating said push-'pull means, force link means connected in said push-pullv means for transmitting the mechanical motion initiated by s aid synchro motor means, said circuit means having a mixing junction, feedback means connected from said synchro motor means to said mixing junction forl picking off "a null signal and nulling the output of sai-d amplifier means, fol-loiwupf follower means connected in parallel with said feedback means for preventingoverrun and hunting of said synchro motor means, said force link means having a housing with a' spring loaded plunger therein for permitting said force link means 'to be contracted and elongated by saidoverf 4ride command movement of said manual control means, differential transformer means in saidvhousing havin-g a .core ladapted to be axially ldisplaced when the length of nneans. is Changed, integrator. means. eonneeted. to integrate said. engeland-signal', said integrator means liaying an. output eleetrieally eenneeted; te said; mixing junction iuopnosition. to saideleetrieal error. signal oi said gyro means, saidl integrator means. supplying said eleetrieal command signal to said mixing junction` aty a` predetermined. rate, aneleetrieal eoruniandsignal of one-Plrase izeing Pielsedofi from saidtr'ansfernier nueans and.' ded to said' integrator. when said foro e link ineens is eontraeted and.. en eleetriealooulnrand sign-al of an opposite phase being pickedoifI Whensaid force linl;1 means is extended uponthe manipulation of said manual control means for overriding said gyroirneans- 3.- A. force link: for. anushfnull. linkage, in an aircraft lCtlitrol. systeniandfeenipiising, a eup=shaped elongated he ingplunger ineansslidably disposed in said housing., 'rstmeans. connected to one external end tof said housing for.. eonneeting. said housing into push-Pull linkage, second' means connected tovv the outer end of' saidiplunge; means forl eonneeting the seme into the .Push-null.. linke age', resiliently eornnressible means eonneeted tol said plunger means, and to said-housing internallyv ofthe latter for.. resisting and limiting, the rnoyernentv of' said plunger means into vand out.' of Vsaid honsing, variable impedance transtornrer rneansdi-snesed in said lhousing and. having anasially-nrovable eoreearried. by said plunger means lfor signallingthepmovement of said plunger meansrinto and out of said housing from aeentral Zero signal'nosie tionin. said housing,

4; A,f,ofr ee link. fora nusliepulllinlsage in an aircraft controlasystenr'andy comprisi1-1g, av cup-shaped elongated housing, plunger rneans slidably disposed in. said housing? first rneanseonneeted to one esterna-l endojfsaid nous: ingfor connecting said-housinginto the push-pullslinlgagee` seeondmeans eonneotedto the outer.. endzui. Said plunger, nieansfor. connecting thesanre inte the pushpulilinlrage, resilientlyieonnpressible means. eonneeted to I husing'frornaeentral zero signal y.position insaid hous- 5- A ytorte linlsv Comprising, a ,sup-shaped `housing hay: ing. a cylindrical Opening formed thereinyegrtfendirigmwar'dly from one outer end thereof, aetubular adusting and preloading screwA threaded intolsaid outerv endA o f said cylindrical opening, a. tubular actuating shaft eo; :axially disposedin saidlcylindrical opening and extending out of saidv housing, rsL and second spring.` retainers slidablydisposed on the innerend of said actuatingshaft, an helioalspring:disposedabout said aetuatingshaft and biais-ing said first and{secondspring retainers, apart, a sleeve disposed aboutsaid actuating shaft andhayirlg .an inner end bearing against said secondlspring retainer, an adjustingfand preloading nuty threaded onto the outer end` of said actuating shaft and bearing. againstthe outer end of said sleeve, a `iirst loclcnut threaded outQthe outer end of said laotuating shaft and hearingagainst said preloading; nut :for locking the same in place, a rod end-memberv` having an eye von theouter.' end thereof, said `rod Vend member being threaded onto the outer end of said actuating shaft, la second flock nut, threaded onto saidvpreloading screw. Iand bearing against theouter end of sadhousing; for. locking said preloading:,screvizr in place, said. Vhousing having annular shoulderl formed therein form-ingthe inner end of said cylindrical opening andA acting as'eatfor saidiirst spring retainer, ,an

annulal; s topjlangey formed en .the inner' end of said actu;v

ating shaftfortretainingsaid ir'st'spxingretainer thereon, a vari-,able impedance transformer xed in; therbottom Vof said housing and having a movable core-coaxially slidable therein, an. adjustable. andature. rody threaded-into Onto tlie outer end: of said. annature red. and; bea ng l against said actuating shaft for locking said amature fed. in glade, said helieal springbiasingl said aetuating Shaft and,l transformer core tok aA centered-zero position and resisting movement thereof axially in either.. dires: tion. and stud bolt means forming aneye threaded into the bottom, of saidphousingwcoaxijal with the eye of rod end member. l

6- A foree linlt eeninrising, ,a.eiinfsliapedlhousing hay.- -ing a oylindrioal` opening, formed. therein extendingin- Wardly. from one outer, end, thereota tubular adjusting and preloading screw, threadedinto saidouter en d ofsaid oylindrioal opening, atnbular aetuating shaft eoaxially disposed in said cylindgjicalopeninggand extending` out of said housing, lirst and, seeondvspring retainers slidably disposed on the inner end ofsaid actuating shaft, aspring disposed about said actuating sllattiand between said Yrs,t and second spring-retainers apant a sleeve disposed about said actuating shaft'land having au inner endr bearing lagainst said second spring retainer, anadjusting andpre loadingnut threaded ontotheouter end of, saidiactuating shaft `andv bearing against the outenendof saidsleeva. a rodlend member havingv -an eye on the outer endfthereof, saidrod endmember :being threaded Qntothe outer` end of' said actuating shaft, said housing haviuganannular shoulder formed therein lforming the innerV end of said Cylilldlvcttlopeniilg andacting as -a4 seat.v for saidrst spring retainer, au annular stopgflange formed. on the inrierend of said actuating shaft for retainingsaidarst thereofheingxed yto said transfornjlerl core, saidlspring biasing saidtactuating shaftlandtransformer core toa centered-zero position andv resisting1 movement` thereof axially inY either7 direction and studQbolt means.y forming anv eye threadedv intothe bottom of said housingcoaxial with the eye of said rod eudfmember.

7. Ajorce comprising, a ,cupef-shapedshousinghav; ing `acylindrioal openingj formed therein,l extending''om one end thereof, a tubularadjusting andpreloadingscrew threaded into. the :outer endjof y said cylindricaL opening, atubular actuating shaft ,coiaxiyally disposed in said cylin'f drical opening and extending. out of said. housing,l first and vsecond spring retainers. slidably Ydisposed `on thefinner erlld. ofsaid actuatingshaft, aspx-ing disposed aboutK said actuating shaft and between said rst `and secondspring retainers, a, sleeve disposed-about said ac tuatinggshaft and having .an inner end `bearing. against saidsecond vspring retainer, al1-adjusting and nreloadingnut threaded.. onto the outer end of saidactuating shaft and bearing against theouter endY of said sleeve, a rod, end A.member-threaded onto the. outer. end of said actuating shaft, said housing halvinggan annular shoulder formed therein, forming the inner,V ndof saidcylindrical opening and forming a. seat for saidfirst spring: retainer, la stop. formed on theinner end'ofsaid lactuatingshaft for retaining said first-spring retaineron said actuating shaft, transformer meansxed inthe bottomof said housing audhaving a movable core slidable therein, anadjustable armattire rodicarried by said actuating shaft with the, inner.endthereofY Ybeing fixed to said 4transformer,core, andsaid springbiasingY said actuating lshafty and transformer coretoa een.tered-zeroy position "andyresisting movement thereof axially ineither Y direction.

pull linkage, second means connected to the outer'ed of said plunger means for connecting the same into the pushpull-pull linkage, resiliently compressible means connected to said plunger means and to said housing internally of the latter for resisting and limiting the movement of said plunger means into and out of said housing, command signal pickoi'f means including transformer means disposed in said housing and having an axially movable core carried by said plunger means forlsignalling the movement of said plunger' means into and out of said housing from a central zero signal position in said housing, adjustable means for limiting the length of travel of said plunger means into and out of said housing.

9. In an aircraft having a control surface, the combination comprising: manual control means including push-pull means for operating and controlling said control surface, automatic pilot means including displacement gyro means adapted to generate an electrical error signal proportional to the displacement of the aircraft from an established reference attitude, amplifier means, circuit means electrically connecting said amplifier means to said gyro means, synchro motor means electrically connected to the output of said amplifier means and having a crank arm operating said push-pull means, force link means connected in said push-pull means for transmitting mechanical motion initiated by said synchro motor means, said circuit means having a mixing junction, feedback means connected from said synchro motor means to said mixing junction for picking off a null signal and nulling the output of said amplier means, follow-up follower means connected in parallel with said feedback means for preventing overrun and hunting of said synchro motor means, said force link means including a cupshaped elongated housing, plunger means slidably disposable in said housing, first means connected to one external end of said housing for connecting said housing into the push-pull linkage, second means connected to the other end of said plunger means for connecting the same into the push-pull linkage, resiliently compressible means connected to said plunger means and to said housing internally of the latter for resisting and limiting movement of said plunger means into and out of said housing, command signal pickoi means including variable impedance transformer means disposed in said housing and having an axially movable core carried by said plunger means for signalling the movement of said plunger means into and of said housing from a central position in said housing whereby said force link means can be contracted and elongated by override command movement of saidmanual control means, integrator means connected to integrate said command signal, said integrator means having an output electrically connected to said mixing junction in opposition to said electrical error signal of said gyro means, said integrator means supplying said electrical command signal to said mixing junction at a predetermined rate, an electrical command signallof one phase being picked off from said transformer means and fed to said integrator When said force link means is contracted and an electrical command signal of an opposite phase being picked ofIr when said force link means is extended upon the manipulation of said manual control means for overriding said automatic pilot means.

i 10. In an aircraft having a control surface, the combination comprising: manual control means including push-pull means for operating and controlling saidV control surface, automatic pilot means including displacement gyro means adapted to generate an electrical error signal proportional kto the displacement of the aircraft from an established reference altitude, amplifier means, circuit means electrically connecting said amplifier means to said gyro means, synchro motor means electrically connected to the output of said amplifier means and having a crank arm operating said push-pull means, force link means connected in said push-pull meansfor transmitting mechanical motion initiated by said synchro motor means, said circuit means having a mixing junction, saidA force link means including a cup-shaped elongated housing having a closed end and an open end, plunger means slidably disposed in said housing, irst means connected to the closed end of said housing for connecting said housing Yto said'manual control means, second means connected to said plunger means for connecting the Asame to vsaid crank armresiliently compressible means connected to said plunger means and to said housinginternally of the latter for resisting and limiting movement of said plunger means into and out of said housing, command signal pickoif means including variable impedance transformer means disposed in saidhousing and having an axially movable core carried by said plunger means for signalling the movement of said plunger means into and out of said housing from a central position in said housing whereby said force link means can be contracted and elongated by override command movement of said manual control means, said force link means including means` for adjusting said compressible means to prevent change in length of said force link means when the tensile or compressional force in said linkage means is `below a predetermined value, integrator means connected to integrate said command signal, said integrator means having an output electrically connected to said mixing junction in opposition to said electrical error signal of saidlgyro means, said integrator means supplying said electrical command signal to said j mixing junction at a predetermined rate, an electrical command signal of one phase being picked off from said transformer means and fed to said integrator When said force link means is contracted and an electrical command signal of an opposite phase being picked oif when said force link means is extended upon the manipulation of said manual control means for overriding said automatic pilot means. l

11. In an aircraft having ya control surface, the combmation comprising: manual control means including linkage means for operating and controllingv said control surface, gyro means adapted to generate an electrical error signal that is a function of the displacement of the aircraft lfrom an established reference condition, amplilier means, circuit means connecting said ampliiier means to said gyro means, synchro motor means driven by the output of said amplifier means and operating said linkage means, force link means connected in said linkage means for transmitting lthe motion initiated by said synchro motor means, mechanical bias means included 1n said force link means preventing change in length 0f said force link means when the tensile or compressional yforce in said linkage means is below a predetermined value, said circuit means having a mixing junction, feedback means connected yfrom said synchro motor means to said mixing junction for picking oif a null signal for nulling the output of said amplifier means, electrical command signal pickoft means in said force link means adapted to pick off a command signal when the length of said force link means is changed by said manual control means, said electrical command signal being representative of change of length and the duration of the vchange of length of said force link means, integrator electrical command signal of one phase being picked oi lfrom said command signal pickotf means and fed to said integrator when said force link means is contracted and an electrical command signal of an opposite phase being picked off when said force link means is extended upon the manipulation of said manual control means for overriding said gyro means.

(References on following page) 11, Referencs Citefdjn the leoi this. patent. 2,590,626 UNIIED; STATES. PATENTS 2,133,168- Gwinn ocr. 11, 1938 895085 22.765843Y Hathaway MBI; 17, 1942 5 2,896,883 2,451,263 Webb 1 Oct.- 12, 194s 

